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	Provedor de dados AgEcon (2) Autor Cranfield, John A.L. (2) Haq, Zahoor Ul (2) Meilke, Karl D. (2) Palavra-chave Agricultural and Food Policy (2) Agrifood Trade (2) Demand and Price Analysis (2) Gravity model (2) Heckman Selection Model (2) International Relations/Trade (2) Marginal effects (2) Selection bias (2) Research Methods/ Statistical Methods (1) Mais... Tipo do documento Working or Discussion Paper (2) Ano 2011 (1) 2010 (1) País United States (2) Idioma Inglês (2)		Ordenar por:  Relevância Autor Título Ano Registros recuperados: 2 Primeira ... 1 ... Última The Gravity Model and the Problem of Zero`s in Agrifood Trade AgEcon Haq, Zahoor Ul; Meilke, Karl D.; Cranfield, John A.L.. and this is a problem when estimating log-linear gravity equations. This has caused many researchers to either ignore the zero trade flows or to replace the zero with a small positive number. Both of these actions bias the resulting parameter estimates of the gravity equation. In this study we correct for this misspecification by using the Heckman selection model to estimate bilateral trade flows for 46 agrifood products, for the period 1990 to 2000, for 52 countries. In our sample, selection bias rarely affects the signs of variables but often has a substantial effect on the magnitude, statistical significance and economic interpretation of the marginal effects. Hence, treating zero trade flows properly is important from both a statistical and an... Tipo: Working or Discussion Paper Palavras-chave: Gravity model; Selection bias; Agrifood Trade; Heckman Selection Model; Marginal effects; Agricultural and Food Policy; Demand and Price Analysis; International Relations/Trade; Research Methods/ Statistical Methods. Ano: 2011 URL: http://purl.umn.edu/116851 Does the Gravity Model Suffer from Selection Bias? AgEcon Haq, Zahoor Ul; Meilke, Karl D.; Cranfield, John A.L.. When analyzing bilateral trade flow data, zero trade flows are quite common and problematic when a gravity equation is estimated with a log-linear functional form. This has caused many researchers to either ignore the zero trade flows or to replace zero with a small positive number. Both of these actions bias the resulting parameter estimates of the gravity equation. In this study we correct for this misspecification by using the Heckman selection model to estimate the bilateral trade flows for 46 agrifood products, for the period 1990 to 2000, for 52 countries. In our sample, selection bias rarely affects the signs of variables but often has a substantial effect on the magnitude, statistical significance and economic interpretation of the marginal... Tipo: Working or Discussion Paper Palavras-chave: Gravity model; Selection bias; Agrifood Trade; Heckman Selection Model; Marginal effects; Agricultural and Food Policy; Demand and Price Analysis; International Relations/Trade. Ano: 2010 URL: http://purl.umn.edu/90884 Registros recuperados: 2 Primeira ... 1 ... Última

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